One model test method by which an actual ship's maneuvering performance can be predicted is the free sailing method. At our ship model basin, the trajectories and yawing angles of model ship were measured during a free sailing model test, and from these values the drift angles of the model ship were calculated. During the analysis, coefficients of the mathematical response model were derived so that simulation calculations could be identified with the time history data of a real ship model test. The proposed mathematical model which includes αr^3 and α_ββ^3 as non-linear terms is as follows.T^'_1T^'_2r^'+(T^'_1+T^'_2)r^'+r^'+α^'r^<'3>=K^'δ^'+K^'T^'_3δ^' T^'_1T^'_2β^'+(T^'_1+T^'_2)β^'+β^'+α^'_ββ^<'3>=K^'_βδ^'+K^'_βT^'_<3β>δ^' The non-linear terms can be presented with hydrodynamic derivatives as follows. α^'≒(N^'_βY^'_<nr>-Y^'_βN^'_<nr>)/C α^'_β≒{-N^'_rY^'_<nβ>+(-m^'-m^'_x+Y^'_r)N^'<nβ>}/C C=N^'_β(-m^'-m^'_x+Y^'_r)-Y^'_βN^'_r We applied this method to a container ship and bulk carrier, and thus confirmed that the method can accurately predict a ship's maneuvering performance.
